Method of transmitting SLSS by V2V terminal

ABSTRACT

The disclosure of the present invention proposes a method for transmitting a sidelink synchronization signal (SLSS). The method may be performed by a vehicle-to-vehicle (V2V) terminal and comprise: performing measurements during a predetermined evaluation time; determining whether values resulting from performing the measurements are below a threshold value; and if the values resulting from performing the measurements during the predetermined evaluation time are below the threshold value, transmitting the SLSS to a neighboring V2V terminal. If the V2V terminal is in radio resource control (RRC) idle state and if the V2V terminal is configured to use 1.28 s or 2.56 s of a discontinuous reception (DRX) cycle length, the V2V terminal may calculate the predetermined evaluation time by using the number of DRX cycles which is not greater than 3.

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. § 119 (e), this application claims the benefit ofU.S. Provisional Application No. 62/315,024, filed on Mar. 30, 2016, thecontents of which are all hereby incorporated by reference herein intheir entirety.

FIELD OF THE INVENTION

The present invention relates to mobile communication.

RELATED ART

3rd generation partnership project (3GPP) long term evolution (LTE)evolved from a universal mobile telecommunications system (UMTS) isintroduced as the 3GPP release 8. The 3GPP LTE uses orthogonal frequencydivision multiple access (OFDMA) in a downlink, and uses singlecarrier-frequency division multiple access (SC-FDMA) in an uplink. The3GPP LTE employs multiple input multiple output (MIMO) having up to fourantennas. In recent years, there is an ongoing discussion on 3GPPLTE-advanced (LTE-A) evolved from the 3GPP LTE.

In LTE/LTE-A, a physical channel of LTE may be classified into adownlink channel, i.e., a PDSCH (Physical Downlink Shared Channel) and aPDCCH (Physical Downlink Control Channel), and an uplink channel, i.e.,a PUSCH (Physical Uplink Shared Channel) and a PUCCH (Physical UplinkControl Channel).

Meanwhile, due to an increase in user requirements for SNS (SocialNetwork Service), communication among terminals physically close to eachother, that is, D2D (Device to Device) communication is required.

D2D communication may be performed among terminals located in coverageof the base station, or among terminals located out of coverage of thebase station. Further, D2D communication may be performed between aterminal located out of coverage of the base station and a terminallocated in coverage of the base station.

The above-mentioned contents on D2D may also be applied tovehicle-to-everything (V2X). The V2X collectively refers tocommunication technology through all interfaces with vehicles. The V2Ximplementations may be, for example, vehicle-to-vehicle (V2V),vehicle-to-infrastructure (V2I), vehicle-to-person (V2P),vehicle-to-network (V2N), or the like.

The V2X terminal may move faster than the D2D terminal. Therefore, thereis a problem in applying the above-described contents on D2D directly tothe V2X.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to solve theabove-mentioned problems.

To achieve the foregoing purposes, the disclosure of the presentinvention proposes a method for transmitting a sidelink synchronizationsignal (SLSS). The method may be performed by a vehicle-to-vehicle (V2V)terminal and comprise: performing measurements during a predeterminedevaluation time; determining whether values resulting from performingthe measurements are below a threshold value; and if the valuesresulting from performing the measurements during the predeterminedevaluation time are below the threshold value, transmitting the SLSS toa neighboring V2V terminal. If the V2V terminal is in radio resourcecontrol (RRC) idle state and if the V2V terminal is configured to use1.28 s or 2.56 s of a discontinuous reception (DRX) cycle length, theV2V terminal may calculate the predetermined evaluation time by usingthe number of DRX cycles which is not greater than 3.

If the V2V terminal is in the RRC idle state and if 1.28 s of the DRXcycle length is used, the V2V terminal may calculate the predeterminedevaluation time by using three (3) DRX cycles.

If the V2V terminal is in the RRC idle state and if 2.56 s of the DRXcycle length is used, the V2V terminal may calculate the predeterminedevaluation time by using two (2) DRX cycles.

If the V2V terminal is in the RRC idle state, the V2V terminal may beconfigured to use 0.32 s or 0.64 s of the DRX cycle length and the V2Vterminal calculates the predetermined evaluation time by using six (6)DRX cycles.

If the V2V terminal is in a RRC connected state, the V2V terminal may beconfigured to use a DRX cycle length which is equal to or less than 0.8s.

If the V2V terminal is in a RRC connected state and if the V2V terminalis configured to use the DRX cycle length satisfying 0.04 s<the DRXcycle length<=1.28 s, the V2V terminal may calculate the predeterminedevaluation time by using three (3) DRX cycles.

If the V2V terminal is in the RRC connected state and if the V2Vterminal is configured to use the DRX cycle length satisfying 1.28 s<theDRX cycle length<=2.56 s, the V2V terminal may calculate thepredetermined evaluation time by using two (2) DRX cycles.

To achieve the foregoing purposes, the disclosure of the presentinvention proposes a vehicle-to-vehicle (V2V) terminal for transmittinga sidelink synchronization signal (SLSS). The V2V terminal may comprise:a transceiver; and a processor operatively to the transceiver andconfigured to: perform measurements during a predetermined evaluationtime; determine whether values resulting from performing themeasurements are below a threshold value; and if the values resultingfrom performing the measurements during the predetermined evaluationtime are below the threshold value, transmit the SLSS to a neighboringV2V terminal. If the V2V terminal is in radio resource control (RRC)idle state and if the V2V terminal is configured to use 1.28 s or 2.56 sof a discontinuous reception (DRX) cycle length, the V2V terminal maycalculate the predetermined evaluation time by using the number of DRXcycles which is not greater than 3.

According to the disclosure of the present invention, the problem of theconventional technology described above may be solved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a wireless communication system.

FIG. 2 illustrates a structure of a radio frame according to FDD in 3GPPLTE.

FIG. 3 illustrates a structure of a downlink radio frame according toTDD in the 3GPP LTE.

FIG. 4 is an exemplary diagram illustrating a resource grid for oneuplink or downlink slot in the 3GPP LTE.

FIG. 5 illustrates a structure of a downlink subframe.

FIG. 6 illustrates the architecture of an uplink sub-frame in 3GPP LTE.

FIG. 7 illustrates the concept of D2D (Device to Device) communicationexpected to be introduced in the next generation communication system.

FIG. 8 illustrates an example of D2D communication or ProSecommunication between UE #1 and UE #2 illustrated in FIG. 7.

FIG. 9 illustrates an example in which UE #2 shown in FIG. 7 selects aRelay UE.

FIG. 10 illustrates an example of transmitting the SLSS.

FIG. 11 is an exemplary diagram of illustrating a concept of V2X.

FIG. 12 illustrates an example in which a V2X device transmits the SLSSaccording to the disclosure of the present description.

FIG. 13 is a block diagram in which a wireless communication system inwhich the disclosure of the present description is implemented.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, based on 3rd Generation Partnership Project (3GPP) longterm evolution (LTE) or 3GPP LTE-advanced (LTE-A), the present inventionwill be applied. This is just an example, and the present invention maybe applied to various wireless communication systems. Hereinafter, LTEincludes LTE and/or LTE-A.

The technical terms used herein are used to merely describe specificembodiments and should not be construed as limiting the presentinvention. Further, the technical terms used herein should be, unlessdefined otherwise, interpreted as having meanings generally understoodby those skilled in the art but not too broadly or too narrowly.Further, the technical terms used herein, which are determined not toexactly represent the spirit of the invention, should be replaced by orunderstood by such technical terms as being able to be exactlyunderstood by those skilled in the art. Further, the general terms usedherein should be interpreted in the context as defined in thedictionary, but not in an excessively narrowed manner.

The expression of the singular number in the present invention includesthe meaning of the plural number unless the meaning of the singularnumber is definitely different from that of the plural number in thecontext. In the following description, the term ‘include’ or ‘have’ mayrepresent the existence of a feature, a number, a step, an operation, acomponent, a part or the combination thereof described in the presentinvention, and may not exclude the existence or addition of anotherfeature, another number, another step, another operation, anothercomponent, another part or the combination thereof.

The terms ‘first’ and ‘second’ are used for the purpose of explanationabout various components, and the components are not limited to theterms ‘first’ and ‘second’. The terms ‘first’ and ‘second’ are only usedto distinguish one component from another component. For example, afirst component may be named as a second component without deviatingfrom the scope of the present invention.

It will be understood that when an element or layer is referred to asbeing “connected to” or “coupled to” another element or layer, it can bedirectly connected or coupled to the other element or layer orintervening elements or layers may be present. In contrast, when anelement is referred to as being “directly connected to” or “directlycoupled to” another element or layer, there are no intervening elementsor layers present.

Hereinafter, exemplary embodiments of the present invention will bedescribed in greater detail with reference to the accompanying drawings.In describing the present invention, for ease of understanding, the samereference numerals are used to denote the same components throughout thedrawings, and repetitive description on the same components will beomitted. Detailed description on well-known arts which are determined tomake the gist of the invention unclear will be omitted. The accompanyingdrawings are provided to merely make the spirit of the invention readilyunderstood, but not should be intended to be limiting of the invention.It should be understood that the spirit of the invention may be expandedto its modifications, replacements or equivalents in addition to what isshown in the drawings.

As used herein, ‘base station’ generally refers to a fixed station thatcommunicates with a wireless device and may be denoted by other termssuch as eNB (evolved-NodeB), BTS (base transceiver system), or accesspoint.

As used herein, ‘user equipment (UE)’ may be stationary or mobile, andmay be denoted by other terms such as device, wireless device, terminal,MS (mobile station), UT (user terminal), SS (subscriber station), MT(mobile terminal) and etc.

FIG. 1 illustrates a wireless communication system.

As seen with reference to FIG. 1, the wireless communication systemincludes at least one base station (BS) 20. Each base station 20provides a communication service to specific geographical areas(generally, referred to as cells) 20 a, 20 b, and 20 c. The cell can befurther divided into a plurality of areas (sectors).

The UE generally belongs to one cell and the cell to which the UE belongis referred to as a serving cell. A base station that provides thecommunication service to the serving cell is referred to as a servingBS. Since the wireless communication system is a cellular system,another cell that neighbors to the serving cell is present. Another cellwhich neighbors to the serving cell is referred to a neighbor cell. Abase station that provides the communication service to the neighborcell is referred to as a neighbor BS. The serving cell and the neighborcell are relatively decided based on the UE.

Hereinafter, a downlink means communication from the base station 20 tothe UE1 10 and an uplink means communication from the UE 10 to the basestation 20. In the downlink, a transmitter may be a part of the basestation 20 and a receiver may be a part of the UE 10. In the uplink, thetransmitter may be a part of the UE 10 and the receiver may be a part ofthe base station 20.

Meanwhile, the wireless communication system may be generally dividedinto a frequency division duplex (FDD) type and a time division duplex(TDD) type. According to the FDD type, uplink transmission and downlinktransmission are achieved while occupying different frequency bands.According to the TDD type, the uplink transmission and the downlinktransmission are achieved at different time while occupying the samefrequency band. A channel response of the TDD type is substantiallyreciprocal. This means that a downlink channel response and an uplinkchannel response are approximately the same as each other in a givenfrequency area. Accordingly, in the TDD based wireless communicationsystem, the downlink channel response may be acquired from the uplinkchannel response. In the TDD type, since an entire frequency band istime-divided in the uplink transmission and the downlink transmission,the downlink transmission by the base station and the uplinktransmission by the terminal may not be performed simultaneously. In theTDD system in which the uplink transmission and the downlinktransmission are divided by the unit of a sub-frame, the uplinktransmission and the downlink transmission are performed in differentsub-frames.

Hereinafter, the LTE system will be described in detail.

FIG. 2 shows a downlink radio frame structure according to FDD of 3rdgeneration partnership project (3GPP) long term evolution (LTE).

The radio frame includes 10 sub-frames indexed 0 to 9. One sub-frameincludes two consecutive slots. Accordingly, the radio frame includes 20slots. The time taken for one sub-frame to be transmitted is denoted TTI(transmission time interval). For example, the length of one sub-framemay be 1 ms, and the length of one slot may be 0.5 ms.

The structure of the radio frame is for exemplary purposes only, andthus the number of sub-frames included in the radio frame or the numberof slots included in the sub-frame may change variously.

Meanwhile, one slot may include a plurality of orthogonal frequencydivision multiplexing (OFDM) symbols. The number of OFDM symbolsincluded in one slot may vary depending on a cyclic prefix (CP). Oneslot includes 7 OFDM symbols in case of a normal CP, and one slotincludes 6 OFDM symbols in case of an extended CP. Herein, since the3GPP LTE uses orthogonal frequency division multiple access (OFDMA) in adownlink (DL), the OFDM symbol is only for expressing one symbol periodin a time domain, and there is no limitation in a multiple access schemeor terminologies. For example, the OFDM symbol may also be referred toas another terminology such as a single carrier frequency divisionmultiple access (SC-FDMA) symbol, a symbol period, etc.

FIG. 3 illustrates the architecture of a downlink radio frame accordingto TD D in 3GPP LTE.

Sub-frames having index #1 and index #6 are denoted special sub-frames,and include a DwPTS(Downlink Pilot Time Slot: DwPTS), a GP(Guard Period)and an UpPTS(Uplink Pilot Time Slot). The DwPTS is used for initial cellsearch, synchronization, or channel estimation in a terminal. The UpPTSis used for channel estimation in the base station and for establishinguplink transmission sync of the terminal. The GP is a period forremoving interference that arises on uplink due to a multi-path delay ofa downlink signal between uplink and downlink.

In TDD, a DL (downlink) sub-frame and a UL (Uplink) co-exist in oneradio frame. Table 1 shows an example of configuration of a radio frame.

TABLE 1 Switch- UL-DL point Subframe index configuration periodicity 0 12 3 4 5 6 7 8 9 0 5 ms D S U U U D S U U U 1 5 ms D S U U D D S U U D 25 ms D S U D D D S U D D 3 10 ms  D S U U U D D D D D 4 10 ms  D S U U DD D D D D 5 10 ms  D S U D D D D D D D 6 5 ms D S U U U D S U U D

‘D’ denotes a DL sub-frame, ‘U’ a UL sub-frame, and ‘S’ a specialsub-frame. When receiving a UL-DL configuration from the base station,the terminal may be aware of whether a sub-frame is a DL sub-frame or aUL sub-frame according to the configuration of the radio frame.

TABLE 2 Normal CP in downlink Extended CP in downlink UpPTS UpPTSSpecial Normal Extended subframe CP in Extended CP Normal CP CP inconfiguration DwPTS uplink in uplink DwPTS in uplink uplink 0  6592 * Ts2192 * Ts 2560 * Ts  7680 * Ts 2192 * Ts 2560 * Ts 1 19760 * Ts 20480 *Ts 2 21952 * Ts 23040 * Ts 3 24144 * Ts 25600 * Ts 4 26336 * Ts  7680 *Ts 4384 * Ts 5120 * ts  5  6592 * Ts 4384 * Ts 5120 * ts  20480 * Ts 619760 * Ts 23040 * Ts 7 21952 * Ts — 8 24144 * Ts —

FIG. 4 illustrates an example resource grid for one uplink or downlinkslot in 3GPP LTE.

Referring to FIG. 4, the uplink slot includes a plurality of OFDM(orthogonal frequency division multiplexing) symbols in the time domainand NRB resource blocks (RBs) in the frequency domain. For example, inthe LTE system, the number of resource blocks (RBs), i.e., NRB, may beone from 6 to 110.

The resource block is a unit of resource allocation and includes aplurality of sub-carriers in the frequency domain. For example, if oneslot includes seven OFDM symbols in the time domain and the resourceblock includes 12 sub-carriers in the frequency domain, one resourceblock may include 7×12 resource elements (REs).

Meanwhile, the number of sub-carriers in one OFDM symbol may be one of128, 256, 512, 1024, 1536, and 2048.

In 3GPP LTE, the resource grid for one uplink slot shown in FIG. 4 mayalso apply to the resource grid for the downlink slot.

FIG. 5 illustrates the architecture of a downlink sub-frame.

In FIG. 5, assuming the normal CP, one slot includes seven OFDM symbols,by way of example.

The DL (downlink) sub-frame is split into a control region and a dataregion in the time domain. The control region includes up to first threeOFDM symbols in the first slot of the sub-frame. However, the number ofOFDM symbols included in the control region may be changed. A PDCCH(physical downlink control channel) and other control channels areassigned to the control region, and a PDSCH is assigned to the dataregion.

The physical channels in 3GPP LTE may be classified into data channelssuch as PDSCH (physical downlink shared channel) and PUSCH (physicaluplink shared channel) and control channels such as PDCCH (physicaldownlink control channel), PCFICH (physical control format indicatorchannel), PHICH (physical hybrid-ARQ indicator channel) and PUCCH(physical uplink control channel).

FIG. 6 illustrates the architecture of an uplink sub-frame in 3GPP LTE.

Referring to FIG. 6, the uplink sub-frame may be separated into acontrol region and a data region in the frequency domain. The controlregion is assigned a PUCCH (physical uplink control channel) fortransmission of uplink control information. The data region is assigneda PUSCH (physical uplink shared channel) for transmission of data (insome cases, control information may also be transmitted).

The PUCCH for one terminal is assigned in resource block (RB) pair inthe sub-frame. The resource blocks in the resource block pair take updifferent sub-carriers in each of the first and second slots. Thefrequency occupied by the resource blocks in the resource block pairassigned to the PUCCH is varied with respect to a slot boundary. This isreferred to as the RB pair assigned to the PUCCH having beenfrequency-hopped at the slot boundary.

The terminal may obtain a frequency diversity gain by transmittinguplink control information through different sub-carriers over time. mis a location index that indicates a logical frequency domain locationof a resource block pair assigned to the PUCCH in the sub-frame.

The uplink control information transmitted on the PUCCH includes an HARQ(hybrid automatic repeat request), an ACK (acknowledgement)/NACK(non-acknowledgement), a CQI (channel quality indicator) indicating adownlink channel state, and an SR (scheduling request) that is an uplinkradio resource allocation request.

The PUSCH is mapped with a UL-SCH that is a transport channel. Theuplink data transmitted on the PUSCH may be a transport block that is adata block for the UL-SCH transmitted for the TTI. The transport blockmay be user information. Or, the uplink data may be multiplexed data.The multiplexed data may be data obtained by multiplexing the transportblock for the UL-SCH and control information. For example, the controlinformation multiplexed with the data may include a CQI, a PMI(precoding matrix indicator), an HARQ, and an RI (rank indicator). Or,the uplink data may consist only of control information.

<Carrier Aggregation (CA>

A carrier aggregation system is described hereinafter.

A carrier aggregation system aggregates a plurality of componentcarriers (CCs). A conventional definition of a cell is changed accordingto carrier aggregation. According to carrier aggregation, a cell maydenote a combination of a downlink component carrier and an uplinkcomponent carrier or a downlink component carrier alone.

Further, in carrier aggregation, cells may be divided into a primarycell, a secondary cell, and a serving cell. A primary cell denotes acell operating at a primary frequency, in which a UE performs an initialconnection establishment procedure or a connection reestablishmentprocedure with a BS or which is designated as a primary cell in ahandover procedure. A secondary cell denotes a cell operating at asecondary frequency, which is configured once RRC connection isestablished and is used to provide an additional radio resource.

As described above, the carrier aggregation system may support aplurality of component carriers (CCs), that is, a plurality of servingcells, unlike a single carrier system.

The carrier aggregation system may support cross-carrier scheduling.Cross-carrier scheduling is a scheduling method for performing resourceallocation for a PDSCH transmitted through a different component carrierthrough a PDCCH transmitted through a specific component carrier and/orresource allocation for a PUSCH transmitted through a component carrierdifferent from a component carrier basically linked with the specificcomponent carrier.

<Discontinuous Reception (DRX)>

Now, DRX will be described.

The discontinuous reception (DRX) is a technique that allows theterminal to discontinuously monitor the downlink channel to reducebattery consumption. When the DRX is set, the terminal discontinuouslymonitors the downlink channel. If not, the terminal continuouslymonitors the downlink channel.

In recent years, a lot of applications require an always-oncharacteristic. Always-on represents a characteristic that the terminalalways accesses the network, and as a result, the terminal mayimmediately transmit data as necessary.

However, when the terminal continuously maintains the network access,the battery consumption is heavy, and as a result, setting the DRXappropriate to the corresponding application may guarantee the always-oncharacteristic while reducing the battery consumption.

The DRX cycle specifies periodic repetition of on-duration in which anavailable period of inactivity is continued. The DRX cycle includes anon-period and an off-period. The on-period is a period in which theterminal monitors the PDCCH within the DRX cycle.

When the DRX is set, the terminal may monitor the PDCCH only during theon-period and not monitor the PDCCH during the off-period.

<D2D(Device to Device) Communication>

On the other hand, the D2D communication expected to be introduced inthe next generation communication system will be described below.

FIG. 7 illustrates the concept of D2D (Device to Device) communicationexpected to be introduced in the next generation communication system.

Due to the increase in user requirements for SNS (Social NetworkService), communication between UEs physically close to each other, thatis, D2D (Device to Device) communication has been required.

In order to reflect the above-described requirements, as illustrated inFIG. 8, it has been discussed that a method which is capable of directlycommunicating without intervention of the base station (eNodeB) 200,among UE #1 100-1, UE #2 100-2, and UE #3 100-3, or UE #4 100-4 UE #5100-5, and UE #6 100-6. Of course, with the help of the base station(eNodeB) 200, it is possible to directly communicate between the UE #1100-1 and the UE #4 100-4. Meanwhile, the UE #4 (100-4) may serve as arepeater for the UE #5 (100-5) and the UE #6 (100-6). Likewise, the UE#1 100-1 may serve as a repeater for UE #2 (100-2) and UE #3 (100-3) farfrom the cell center.

Meanwhile, D2D communication is also called Proximity Service (ProSe).The UE performing the proximity service is also referred to as a ProSeUE. Further, a link among UEs used in the D2D communication is alsoreferred to as a side link. A frequency band that may be used for theside link is as follows.

TABLE 3 E-UTRA Transmission Reception Duex Side link band band F_(UL)_(—) _(low)-F_(UL) _(—) _(high) F_(DL) _(—) _(low)-F_(DL) _(—) _(high)mode 2 2 1850 MHz-1910 MHz 1850 MHz-1910 MHz HD 3 3 1710 MHz-1785 MHz1710 MHz-1785 MHz HD 4 4 1710 MHz-1755 MHz 1710 MHz-1755 MHz HD 7 7 2500MHz-2570 MHz 2500 MHz-2570 MHz HD 14 14 788 MHz-798 MHz 788 MHz-798 MHzHD 20 20 832 MHz-862 MHz 832 MHz-862 MHz HD 26 26 814 MHz-849 MHz 814MHz-849 MHz HD 28 28 703 MHz-748 MHz 703 MHz-748 MHz HD 31 31 452.5MHz-457.5 MHz 452.5 MHz-457.5 MHz HD 41 41 2496 MHz-2690 MHz 2496MHz-2690 MHz HD

Physical channels used for the sidelink are as follows.

-   -   PSSCH (Physical Sidelink Shared Channel)    -   PSCCH (Physical Sidelink Control Channel)    -   PSDCH (Physical Sidelink Discovery Channel)        -   PSBCH (Physical Sidelink Broadcast Channel)

Further, physical signals used in the side link are as follows.

-   -   DMRS (Demodulation Reference signal)    -   SLSS (Sidelink Synchronization signal)

The SLSS includes a PSLSS (primary sidelink synchronization signal) anda SSLSS (secondary sidelink synchronization signal).

FIG. 8 illustrates an example of D2D communication or ProSecommunication between UE #1 and UE #2 illustrated in FIG. 7.

Referring to FIG. 8, the BS 200 broadcasts a System Information Block(SIB) in a cell.

The SIB may include information on resource pools related to D2Dcommunication. Information on the resource pool related to the D2Dcommunication may be divided into SIB type 18 and SIB type 19.

The SIB type 18 may include resource configuration information for D2Dcommunication. Further, the SIB type 19 may include resource settinginformation related to a D2D discovery.

The SIB type 19 includes the discSyncConfig as shown below.

TABLE 4 SIB Type 19 discSyncConfig Indicates a configuration as towhether the UE is allowed to receive or transmit synchronizationinformation. The base station (E-UTRAN) can set discSyncConfig when theUE intends to transmit synchronization information using dedicatedsignaling when it intends to use the dedicated signaling to allow

The discSyncConfig includes SL-SyncConfig. The SL-SyncConfig includesconfiguration information for SLSS reception and SLSS transmission asshown in the following table.

TABLE 5 SL-SyncConfig field description discSyncWindow Also called asearching window. Indicates a synchronization window in which the UEexpects the SLSS. The value can be set to w1 or w2. The value w1represents 5 milliseconds, and the value w2 corresponds to the length ofthe normal CP divided by 2. syncTxPeriodic Indicates whether the UEtransmits the SLSS once or periodically (e.g. every 40 ms) within eachperiod of a discovery signal transmitted by the UE. For the periodictransmissions, the UE also transmits a MasterInformationBlock-SL.syncTxThreshIC Represents a threshold used when in coverage. If the RSRPvalue measured for the counterpart UE (recognized as a cell) selectedfor sidelink communication is lower than the threshold value, the UE maytransmit the SLSS for the sidelink communication with the counterpartUE. txParameters Includes a parameter for a configuration fortransmission.

Meanwhile, the UE #1 100-1 located within the coverage of the basestation 200 establishes an RRC connection with the base station.

Further, the UE #1 100-1 receives an RRC message, e.g., an RRCConnection Reconfiguration message from the BS 200. The RRC messageincludes a discovery configuration (hereinafter referred to as adiscConfig). The discConfig includes configuration information for adiscover resource pool (hereinafter referred to as a DiscResourcePool)for discovery. The DiscResourcePool includes information as shown in thefollowing table.

TABLE 6 DiscResourcePool discPeriod May be noted as a discovery period,and is also called a PSDCH period, as a period of resources allocated ina cell for transmission/reception of a discovery message. The values maybe rf32, rf64, rf128, rf256, rf512, rf1024, or the like. These valuesrepresent the number of radio frames. That is, when the value is rf32,it represents 32 radio frames. numRepetition Indicates the number oftimes that the subframe Bitmap is repeated for mapping to the subframeoccurred in the discPeriod. The base station configures numRepetitionand subframeBitmap so that the mapped subframe ca not exceed thediscPeriod. TF-ResourceConfig Assigns a set of time/frequency resourceused in the sidelink communication.

The TF-ResourceConfig includes information as shown in the followingtable.

TABLE 7 SL-TF-ResourceConfig-r12 ::= SEQUENCE {   prb-Num-r12   INTEGER(1..100),   prb-Start-r12 INTEGER (0..99),   prb-End-r12   INTEGER(0..99),   offsetIndicator-r12 SL-OffsetIndicator-r12,  subframeBitmap-r12 SubframeBitmapSL-r12 }

The SubframeBitmapSL is as in the following table.

TABLE 8 SubframeBitmapSL May be noted as discoverySubframeBitmap, andassingns a subframe bitmap indicating the resources used for the sidelink. The value may be designated as bs4, bs8, bs12, bs16, bs30, bs40,bs40, or the like. For example, the bs40 refers to a bit string lengthof 40.

The SL-OffsetIndicator includes information as shown in the followingtable.

TABLE 9 SL-OffsetIndicator May be noted as discoveryOffsetIndicator, andindicates an offset in a first period of the resource pool within theSFN cycle. SL-OffsetIndicatorSync May be noted as SyncOffsetIndicator,indicates the relationship between subframes and SFNs containingsynchronous resources based on an equation (SFN * 10 + Subframe Number)mod 40 = SL-OffsetIndicatorSync.

Meanwhile, the UE #1 100-1 may transmit a discovery signal through thePSDCH in order for the UE #1 to detect whether there is a suitable UE inthe vicinity thereof for D2D communication or ProSe communication, orinform its presence.

Also, the UE #1 100-1 may transmit a scheduling assignment (SA) throughthe PSCCH. The UE #1 100-1 may transmit a PSSCH including data based onthe scheduling assignment (SA).

FIG. 9 illustrates an example in which UE #2 shown in FIG. 7 selects aRelay UE.

Referring to FIG. 9 along with FIG. 7, the UE #2 100-2 located outsidethe coverage of the base station receives the discovery signal fromneighboring UEs and a DMRS for demodulation of the discovery signal, inorder to communicate with the UE #1 100-1 which is located within thecoverage of the base station and thus operates as the Relay UE. Also,the UE #2 100-2 receives a PSBCH from the neighboring UEs and a DMRS fordemodulating the PSBCH.

Then, the UE #2 100-2 performs a measurement based on the receivedsignals.

The measurement includes a measurement of S-RSRP (Sidelink ReferenceSignal Received Power) and a measurement of SD-RSRP (Sidelink DiscoveryReference Signal Received Power).

Here, the S-RSRP means an average received power on an RE (ResourceElement) including a DMRS for demodulating a PSBCH received in themiddle six PBBs. In this case, the power per RE is determined from theenergy received on the portion excluding the CP portion in the OFDMsymbol.

The SD-RSRP means the average reception power on the RE including theDMRS for demodulating the PSDCH, when the CRC check is successful inaccordance with successful decoding of the PSDCH including the discoverysignal.

Upon completion of the measurement, the UE #2 100-2 selects the UE #1100-1 capable of operating as the Relay UE based on the measurementresult, that is, the measurement result of the SD-RSRP.

FIG. 10 illustrates an example of transmitting the SLSS.

Referring to FIG. 10, UE #1 100-1 located in coverage (IC) of the basestation receives SLSS configuration information (e.g., SL-SyncConfigshown in Table 5). The SLSS configuration information may include afirst threshold value, e.g., syncTxThreshIC, for determining whether ornot to transmit the SLSS in coverage (IC), as shown in Table 5.

The UE #1 (100-1) located in coverage (IC) performs the RSRP measurementduring the first threshold (e.g., syncTxThreshIC). Then, the UE #1 100-1determines whether the measured value of the RSRP is lower than thefirst threshold value (e.g., syncTxThreshIC). If the measured value ofthe RSRP is smaller than the first threshold value (e.g.,syncTxThreshIC) during a predetermined evaluation time (e.g.,T_(evaluate,SLSS)), the UE #1 100-1 transmits SLSS.

Meanwhile, the illustrated UE #2 100-2 and UE #3 100-3 are currently outof coverage (OoC). The UE #2 100-2 and the UE #3 100-3 is storingpredetermined information, e.g., SL-Preconfiguration. TheSL-Preconfiguration may include a synchronization signal, i.e.,SL-PreconfigSync, which is previously configured on the SLSStransmission. More specifically, the SL-PreconfigSync may include asecond threshold value, e.g., syncTxThreshOoC, for determining whetherthe SLSS is transmitted from out of coverage (OoC) area.

The UE #2 100-2 located out of coverage (OoC) performs RSRP measurementduring a predetermined evaluation time (e.g., T_(evaluate,SLSS)). Then,the UE #2 100-2 determines whether the measured value of the RSRP islower than the second threshold value (e.g., syncTxThreshOoC). If themeasured value of the RSRP is smaller than the second threshold value(e.g., syncTxThreshOoC) during the predetermined evaluation time (e.g.,T_(evaluate,SLSS)), the UE #2 100-2 transmits SLSS.

<V2X(Vehicle-to-Everythihg)>

The above-mentioned D2D may also be applied to vehicle-to-everything(V2X). The V2X collectively refers to communication technology throughall interfaces with vehicles. The implementation of V2X may be asfollows.

First, in the V2X, ‘X’ may be a vehicle (VEHICLE). In this case, the V2Xmay be referred to as vehicle-to-vehicle (V2V), which may meancommunication between vehicles.

FIG. 11 is an exemplary diagram of illustrating a concept of V2X.

As may be seen with reference to FIG. 10, the vehicles (i.e., wirelessdevices mounted on the vehicle) 100-1, 100-2, and 100-3 can communicatewith each other.

Meanwhile, in V2X, ‘X’ can mean a person (Person) or a pedestrian(PEDESTRIAN). In this case, V2X may be represented as vehicle-to-personor vehicle-to-pedestrian (V2P). Here, the pedestrian is not necessarilylimited to a person walking on a pedestrian, and may include a personriding a bicycle, a driver or a passenger of a vehicle (with a speedlower than a certain speed).

Or ‘X’ may be an infrastructure (Infrastructure)/network(Network). Inthis case, the V2X may be referred to as vehicle-to-infrastructure (V2I)or vehicle-to-network (V2N) and may refer to the communication betweenthe vehicle and the ROADSIDE UNIT (RSU) or between the vehicle and thenetwork. The roadside apparatus may be a transportation-relatedinfrastructure, e.g., an apparatus for indicating speed. The roadsideapparatus may be implemented in a base station or a fixed terminal.

Meanwhile, the V2X terminal may move at a high speed than the D2Dterminal. Therefore, there is a problem in applying the above-describedD2D contents directly to V2X. More specifically, since the predeterminedevaluation time (e.g., T_(evaluate,SLSS)) related to the comparison ofthe measured value of the RSRP with the first or second threshold valuehas been established in consideration of the conventional low-speedmovement, it is difficult to apply it to the V2X terminal moving at ahigh speed.

<Disclosure of the Present Description>

Accordingly, the disclosure of the present description proposes methodsto solve the above-mentioned problems.

For the predetermined time (e.g., T_(evaluate,SLSS)) described above, ithas been conventionally divided into as the cases that the UE is in theRRC Connected state in coverage (IC), the UE is in the RRC idle state incoverage (IC), an the UE is located out of coverage (OoC) area.

First, when the UE is in the RRC Connected state in the IC (Coverage),the T_(evaluate,SLSS) have been determined as shown in the followingtable.

TABLE 10 T_(evaluate,SLSS) DRX cycle length [s] [s] (number of DRXcycles) 0.32 1.92 (6) 0.64 3.84 (6) 1.28 7.68 (6) 2.56 15.36 (6) 

The number in parentheses in the above table means the number of DRXcycles. For example, 1.92 (6) in the first row means 6 DRX cycles in1.92 seconds. That is, when the T_(evaluate,SLSS) are 1.92 seconds, itmeans that six times of the DRX cycle of 0.32 length is required forRSRP measurement. In addition, if the T_(evaluate,SLSS) are 15.36seconds, it means that six times of the DRX cycle of length 2.56 isrequired for RSRP measurement.

Meanwhile, if the UE is in the RRC idle state in converge (IC), theT_(evaluate,SLSS) are determined as shown in the following table.

TABLE 11 T_(evaluate,SLSS) DRX cycle length [s] [s] (number of DRXcycles) ≤0.04 0.4 (Note 1) 0.04 < DRX-cycle ≤ 2.56 Note 2 (6) (Note 1):Number of DRX cycles depends upon the DRX cycle in use Note 2: Timedepends upon the DRX cycles in use

On the other hand, when the UE is located out of coverage (OoC), theT_(evaluate,SLSS) are determined as follows.

-   -   T_(evaluate,SLSS) with ProSe Direct Communication=800 ms

As described above, the T_(evaluate,SLSS) for out of coverage (OoC) havebeen determined to be 800 ms. Here, it may be considered that a relativespeed is 250 km/h. For example, if the V2X terminal A moves at 125 km/hand the V2X terminal B moves at 125 km/h in the opposite direction, therelative speed is 250 km/h. In this case, a relative movement distanceis 111 m during 800 ms, which is the evaluation time(T_(evaluate,SLSS)). Therefore, there is no problem on using theT_(evaluate,SLSS) for out of coverage as it is.

On the other hand, let's assume that in the RRC connection state, theV2X terminal moves at a speed of 120 km/h. Then, the V2X terminal willmove 512 meters for 15.35 seconds. If the V2X terminal moves at a speedof 250 km/h, for calculating a travelling distance, it is as shown inthe table

TABLE 12 DRX cycle length Tevaluate, SLSS Moving distance with [s] [s](number of DRX cycles) 250 km/h [m] 0.32 1.92 (6) 133 0.64 3.84 (6) 2671.28 7.68 (6) 533 2.56 15.36 (6)  1067

As shown in the above table, when the V2X terminal moves at a speed of250 km/h, the V2X terminal moves about 1 km during 15.35 seconds (s).Further, since a serving cell will change while the V2X terminal moves 1km, it is meaningless to measure the RSRP to determine whether totransmit the SLSS.

Therefore, it is necessary to improve the evaluation timeT_(evaluate,SLSS) which has been conventionally determined. Accordingly,the present description proposes as follows.

Proposal 1: Considering a V2X terminal moving at high speed, it isproposed to use only 0.32 s (i.e., 320 ms) and 0.64 s (i.e., 640 ms) forthe DRX cycle length for the RSRP evaluation time to determine whetherto transmit the SLSS.

Proposal 2: It is proposed to use the existing evaluation time when theDRX cycle length is 0.32 s (i.e., 320 ms) and 0.64 s (i.e., 640 ms),while it is proposed to reduce the number of DRX cycles when the DRXcycle length is 1.28 s or 2.56 s.

The above two proposals may be applied to both the RRC connection stateand the RRC idle state.

Specifically, according to proposal 1 in the RRC idle state, theevaluation time T_(evaluate,SLSS) may be determined as follows

TABLE 13 T_(evaluate,SLSS) DRX cycle length [s] [s] (number of DRXcycles) 0.32 1.92 (6) 0.64 3.84 (6) 1.28 7.68 (6) 2.56 15.36 (6)  Note1: For V2X service, DRX cycle length of 0.32 s and 0.64 s are appliedfor T_(evaluate,SLSS).

As may be seen in note 1 above, according to proposal 1 in the RRC idlestate, only the DRX cycle lengths 0.32 s and 0.64 s may be used to makeshort the evaluation time T_(evaluate,SLSS).

Alternatively, according to proposal 2 in the RRC idle state, theevaluation time T_(evaluate,SLSS) may be determined as follows.

TABLE 14 T_(evaluate,SLSS) DRX cycle length [s] [s] (number of DRXcycles) 0.32 1.92 (6) 0.64 3.84 (6) 1.28 3.84 (3) 2.56 5.02 (2)

As may be seen from the above table, according to proposal 2 in the RRCidle state, if the DRX cycle length is 1.28 s or 2.56 s, the evaluationtime T_(evaluate,SLSS) may be made shortened by reducing the number ofDRX cycles.

Meanwhile, according to proposal 1 in the RRC connection state, theevaluation time T_(evaluate,SLSS) may be determined as follows

TABLE 15 T_(evaluate,SLSS) DRX cycle length [s] [s] (number of DRXcycles) ≤0.04 0.4 (Note 1) 0.04 < DRX-cycle ≤ 2.56 Note 2 (6) (Note 1):Number of DRX cycles depends upon the DRX cycle in use Note 2: Timedepends upon the DRX cycles in use Note 3: For V2X service, DRX cyclelength which is equal to and less than 0.8 s is applied forT_(evaluate,SLSS).

As may be seen from note 3 above, according to Proposal 1 in the RRCconnection state, only the 0.32 s and 0.64 s of DRX cycle lengths lessthan 0.8 s may be used to make the evaluation time T_(evaluate,SLSS)shorten.

Meanwhile, according to proposal 2 in the RRC connection state, theevaluation time T_(evaluate,SLSS) may be defined as follows.

TABLE 16 T_(evaluate,SLSS) DRX cycle length [s] [s] (number of DRXcycles) ≤0.04 0.4 (Note 1) 0.04 < DRX-cycle ≤ 1.28 Note 2 (3) 1.28 <DRX-cycle ≤ 2.56 Note 2 (2) Note 1: Number of DRX cycles depends uponthe DRX cycle in use Note 2: Time depends upon the DRX cycles in use

As may be seen from the above table, according to Proposal 2 in the RRCconnection state, if the DRX cycle length is 1.28 s or 2.56 s, theevaluation time T_(evaluate,SLSS) may be made shortened by reducing thenumber of DRX cycles.

FIG. 12 illustrates an example in which a V2X device transmits the SL SSaccording to the disclosure of the present description.

Referring to FIG. 12, the V2X terminal #1 100-1 located in the coverage(IC) of the base station receives configuration information of the SLSS(e.g., SL-SyncConfig shown in Table 5). The SLSS configurationinformation may include a first threshold value, e.g., syncTxThreshIC,for determining whether or not to transmit the SLSS in coverage (IC), asshown in Table 5.

The V2X terminal #1 100-1 located in coverage (IC) of the base stationperforms the RSRP measurement during the reduced evaluation time (e.g.,T_(evaluate,SLSS)). Further, the V2X terminal #1 100-1 determineswhether the measured value of the RSRP is lower than the first thresholdvalue (e.g., syncTxThreshIC). If the measured value of the RSRP issmaller than the first threshold value (e.g., syncTxThreshIC) during theshortened evaluation time (e.g., T_(evaluate,SLSS)), the V2X terminal #1100-1 transmits SLSS.

When the V2X terminal #1 100-1 is in the RRC idle state, the DRX cyclelength may be 0.32 s (i.e., 320 ms) and 0.64 s (i.e., 640 ms) to makeshorten the evaluation time as the proposal 1, or when the DRX cyclelength is 1.28 s or 2.56 s as the proposal 2, the evaluation time may bemade shortened by reducing the number of DRX cycles.

When the V2X terminal #2 100-1 is in the RRC connected state, only the0.32 s (i.e., 320 ms) and 0.64 s (i.e., 640 ms) of the DRX cycle lengthlees than 0.8 ms may be used to make shorten the evaluation time as theproposal 1, when the DRX cycle length is 1.28 s or 2.56 s as theproposal 2, the evaluation time may be made shortened by reducing thenumber of DRX cycles.

As described above, the embodiments of the present invention may beimplemented by various means. For example, embodiments of the presentinvention may be implemented by hardware, firmware, software, or acombination thereof. More specifically, it will be described withreference to the drawings.

FIG. 13 is a block diagram in which a wireless communication system inwhich the disclosure of the present description is implemented.

A base station 200 includes a processor 210, a memory 220 and a radiofrequency (RF) unit 930. The memory 920 is connected to the processor210 and stores a variety of information to operate the processor 210.The RF unit 203 connected to the processor 201 to transmit and/orreceive a radio signal. The processor 201 implements the proposedfunctionality, process and/or method. In the above-described embodiment,the operation of the base station may be implemented by the processor201.

A terminal 100 includes a processor 101, a memory 102, and an RF unit103. The memory 102 is connected to the processor 101 and stores variousinformation for driving the processor 101. The RF unit 103 is connectedto the processor 101 to transmit and/or receive a radio signal. Theprocessor 101 implements the proposed functions, procedures and/ormethods.

The processors may include application-specific integrated circuit(ASIC), other chipset, logic circuit and/or data processing device. Thememories may include read-only memory (ROM), random access memory (RAM),flash memory, memory card, storage medium and/or other storage device.The RF unit may include baseband circuitry to process radio frequencysignals. When the embodiments are implemented in software, thetechniques described herein can be implemented with modules (e.g.,procedures, functions, and so on) that perform the functions describedherein. The modules can be stored in memories and executed byprocessors. The memories can be implemented within the processors orexternal to the processors 810, 910 in which case those can be coupledto the processors 810, via various means as is known in the art.

In the exemplary system described above, although the methods aredescribed on the basis of a flowchart as a series of steps or blocks,the present invention is not limited to the order of the steps, and somesteps may occur in different orders or simultaneously with other stepsas shown above. It will also be understood by those skilled in the artthat the steps shown in the flowchart are not exclusive, and that othersteps may be included or that one or more steps in the flowchart may bedeleted without affecting the scope of the invention.

What is claimed is:
 1. A method for transmitting a sidelinksynchronization signal (SLSS), the method performed by avehicle-to-everything (V2X) terminal and comprising: performingmeasurements during an evaluation time; determining whether at least onevalue resulting from performing the measurements are below a thresholdvalue; and if the at least one value resulting from performing themeasurements during the evaluation time is below the threshold value,transmitting the SLSS to a neighboring V2X terminal, wherein if the V2Xterminal is in a radio resource control (RRC) idle state and if the V2Xterminal is configured to use 2.56 s of a discontinuous reception (DRX)cycle length, the V2X terminal calculates the evaluation time by usingthe number of DRX cycles which is not greater than 3, and wherein if theV2X terminal is in the RRC idle state and if 1.28 s of the DRX cyclelength is used, the V2X terminal calculates the evaluation time by usingthree (3) DRX cycles.
 2. The method of claim 1, wherein if the V2Xterminal is in the RRC idle state and if 2.56 s of the DRX cycle lengthis used, the V2X terminal calculates the evaluation time by using two(2) DRX cycles.
 3. The method of claim 1, wherein if the V2X terminal isin the RRC idle state, the V2X terminal is configured to use 0.32 s or0.64 s of the DRX cycle length and the V2X terminal calculates theevaluation time by using six (6) DRX cycles.
 4. The method of claim 1,wherein if the V2X terminal is in a RRC connected state, the V2Xterminal is configured to use a DRX cycle length which is equal to orless than 0.8 s.
 5. The method of claim 1, wherein if the V2X terminalis in a RRC connected state and if the V2X terminal is configured to usethe DRX cycle length satisfying 0.04 s<the DRX cycle length<=1.28 s, theV2X terminal calculates the evaluation time by using three (3) DRXcycles.
 6. The method of claim 5, wherein if the V2X terminal is in theRRC connected state and if the V2X terminal is configured to use the DRXcycle length satisfying 1.28 s<the DRX cycle length<=2.56 s, the V2Xterminal calculates the evaluation time by using two (2) DRX cycles. 7.A vehicle-to-everything (V2X) terminal for transmitting a sidelinksynchronization signal (SLSS), the V2X terminal comprising: atransceiver; and a processor operatively connected to the transceiverand configured to: perform measurements during an evaluation time,determine whether at least one value resulting from performing themeasurements is below a threshold value, and if the at least one valueresulting from performing the measurements during the evaluation time isbelow the threshold value, transmit the SLSS to a neighboring V2Xterminal, wherein if the V2X terminal is in radio resource control (RRC)idle state and if the V2X terminal is configured to use 2.56 s of adiscontinuous reception (DRX) cycle length, the processor calculates theevaluation time by using the number of DRX cycles which is not greaterthan 3, and wherein if the V2X terminal is in the RRC idle state and if1.28 s of the DRX cycle length is used, the processor calculates theevaluation time by using three (3) DRX cycles.
 8. The V2X terminal ofclaim 7, wherein if the V2X terminal is in the RRC idle state and if2.56 s of the DRX cycle length is used, the processor calculates theevaluation time by using two (2) DRX cycles.
 9. The V2X terminal ofclaim 7, wherein if the V2X terminal is in the RRC idle state, the V2Xterminal is configured to use 0.32 s or 0.64 s of the DRX cycle lengthand the processor calculate the evaluation time by using six (6) DRXcycles.
 10. The V2X terminal of claim 7, wherein if the V2X terminal isin a RRC connected state, the processor is configured to use a DRX cyclelength which is equal to or less than 0.8 s.
 11. The V2X terminal ofclaim 7, wherein if the V2X terminal is in a RRC connected state and ifthe processor is configured to use the DRX cycle length satisfying 0.04s<the DRX cycle length<=1.28 s, the processor calculates the evaluationtime by using three (3) DRX cycles.
 12. The V2X terminal of claim 11,wherein if the V2X terminal is in the RRC connected state and if the V2Xterminal is configured to use the DRX cycle length satisfying 1.28 s<theDRX cycle length<=2.56 s, the processor calculates the evaluation timeby using two (2) DRX cycles.